1. Field of the Invention
The present invention relates to a semiconductor sensor such as a semiconductor accelerometer or a semiconductor gyroscope that uses a piezo-resistive element.
2. Description of the Related Art
A semiconductor sensor may be used to measure the acceleration in the traveling direction or in the lateral direction of a moving vehicle, or to measure the shaking of a video camera.
One type of semiconductor sensor may have a piezo-resistive element fabricated on the surface of a silicon single crystal wafer through an IC (integrated circuit) fabrication process, and this piezo-resistive element may be used as a strain gauge (e.g., see Japanese Patent No. 2670048, Japanese Laid-Open Patent Application No. 2004-233080, and Japanese Laid-Open Patent Application No. 2004-257832). Such a semiconductor sensor using the piezo-resistive element includes a thin-walled beam that may be realized by creating concave portions through etching on the rear face of the silicon wafer at the region where the piezo-resistive element is arranged, for example. The beam is configured to deform in response to acceleration, and in turn, the resistance of the piezo-resistive element may change according to the deformation of the beam so that an electric signal corresponding to the acceleration may be obtained.
Also, a proof mass is attached to the beam at one side to facilitate deformation of the beam. The end of the beam at the other side that is opposite from the side that is attached to the proof mass is connected to a support element. The support element includes plural metal wiring patterns and plural pad electrodes that are electrically connected to the piezo-resistive element.
Also, a cover plate may be arranged over the beam and the proof mass to control the moving distance of the proof mass so as to prevent the beam from receiving a large impact and being damaged, the cover plate being spaced apart from the beam and the proof mass by a predetermined distance (e.g., see Japanese Laid-Open Patent Publication No. 2004-233072).
In the semiconductor sensor as is disclosed in Japanese Laid-Open Patent Publication No. 2004-233072, small concave portions are arranged at plural locations on the surface of the support element to which the flexible element is connected, the depth of the concave portions being arranged to be smaller than the diameter of spherical spacers that are mixed into a silicon rubber resin material, and the cover plate is arranged to be fixed to the support element at the concave portions so that the cover plate may be arranged over the beam and the proof mass.
It is noted that in the case of arranging the cover plate on the beam and the proof mass, when a region dedicated to fixing the cover plate to the support element is provided, the chip area of the semiconductor sensor may be increased.